The present disclosure relates to an electro-wetting device utilizing an electro-wetting effect (electro-capillary phenomenon), and a method of manufacturing the same.
In recent years, a development of an electro-wetting device utilizing an electro-wetting effect has been advanced (for example, refer to a pamphlet of PCT Patent Publication No. WO 99/18456). The electro-wetting effect means a phenomenon that when a voltage is applied across a liquid having a conductivity and an electrode, an energy of a solid-liquid interface between the electrode surface and the liquid changes, and thus a shape of the liquid surface changes.
In general, the electro-wetting device includes a conductive first liquid, an insulating second liquid, a pair of base materials (a lower substrate, and an upper substrate) defining a liquid room for accommodating therein the first and second liquids, an electrode layer formed on a surface of the lower substrate, and an insulating layer formed on a surface of the electrode layer (for example, refer to Japanese Patent Laid-Open No. 2003-302502). A voltage is applied across the conductive first liquid and the electrode layer between which the insulating layer is sandwiched, which results in that a shape of an interface between the first and second liquids changes due to an electro-wetting effect. Thus, refractive indices of the first and second liquids are made different from each other, whereby it is possible to structure a variable focusing lens in which a shape of an interface between the two liquids reversibly changes in accordance with a magnitude of the applied voltage.
In recent years, the development of the electro-wetting device, having high reliability, which is driven with a low drive voltage is required. As described above, the electro-wetting device is driven in accordance with the magnitude of the voltage applied across the conductive liquid and the electrode layer. The drive voltage is proportional to a dielectric constant of the insulating layer interposed between the conductive liquid and the electrode layer, and is inversely proportional to a thickness of the insulating layer. Therefore, a high-dielectric constant material is formed as the insulating layer to have a small thickness, thereby making it possible to reduce the drive voltage for the electro-wetting device. Here, a sputtered film or the like made of an insulating inorganic crystalline material such as a metal oxide is known as an insulating material having a high dielectric constant.
However, since irregularities of a film surface after film deposition are relatively large in this sort of inorganic material, this sort of inorganic material involves a problem that the uniformity of a film thickness is poor, and thus it is difficult to obtain the stable withstand voltage characteristics. That is to say, the possibility that current leakage occurs between a local area having peak irregularities of the high-dielectric constant film formed, and a conductive liquid, and thus dielectric breakdown of an insulating layer occurs becomes high.
Therefore, it is desired to provide an electro-wetting device which is capable of ensuring a highly reliable insulating structure by preventing withstand voltage characteristics from being deteriorated due to use of a high-dielectric constant film, and a method of manufacturing the same.